Post-fire juvenile period of plants in south-west Australia forests and implications for fire management

Regular prescribed burning to manage the accumulation of flammable live and dead vegetation (fuel) is a strategy for ameliorating wildfire impacts in fire-prone environments. The interval between prescribed fires needs to be sufficient to manage fuel accumulation but it should also be ecologically acceptable. Time to first flowering after fire (juvenile period) is a biological indicator that can be used to guide minimum intervals between fires to conserve plant diversity. A survey of 639 plant species in forests and associated ecosystems of south-west Western Australian revealed that 97% of understorey species reached flowering age within 3 years of fire and all species reached flowering age within 5 years of fire. Within species variation was evident, with plants at the drier end of their range taking longer to reach flowering age. Fire sensitive plants, being obligate seeder species with longer juvenile periods (> 3 years), mostly occurred in low rainfall zones so took longer to mature, or in habitats that were less prone to fire because they remained moist for a longer period or because surface fuels were inherently sparse and discontinuous. Due to uncertainty about the reproductive biology and seed bank dynamics of most of the flora, we recommend that the conservative minimum interval between fires that are lethal to fire sensitive plants is about twice the juvenile period of the slowest maturing species in the community. Occasional landscape fires at shorter intervals would be ecologically acceptable only if these fires were of a sufficiently low intensity as to not kill plants with long juvenile periods, or were patchy and did not burn the habitats in which they occur.